Variable pitch propeller



Dec. 13, 1932. E, N 1,890,932

VARIABLE PITCH PROPELLER Original Filed Jan. 6. 1928 2 Sheets-Sheet l l/5L R F\ L V Wilde a4 hzl 9/422 J 1:

Dec. 13, 1932 BR|NE 1,890,932

VARIABLE PITCH PROPELLER Original Filed Jan. 6. 1928 2 Sheets-Sheet 2vwento'c Patented Dec. 13,, 1932 PATENT. OFFICE EMIL A. BRINER, OF EASTORANGE, NEW JERSEY VARIABLE PITCH PROIPELLER Original application filedJanuary 6, 1928. Serial No. 244,829. Divided and this application filedApril 28,

' 1929. Serial No. 358,387. a

This is a division of my application, Serial their own axis. That, initself, has been done.

My object is to provide a construction that is more than a mere pictureof something that can be manufactured and be made to workexperimentally, and then quickly wear out in actual commercial service.That also has been done. Such can hardly be said to be usefulinventions.

My object is more than that. It is to pro vide a construction, and modeof operation, so simple as to stand up under the actual, diflicultconditions of serv ce. Such conditions include the high revolutionsrequired by commercial airplane engines, and the severe vibration of theengine and its mounting. Then there is a tuning fork, and twistingeffect, called flutter, incident to actual use.

All these conditions must be met with maximum simplicity to keep downthe first cost, weight, and maintenance expense.

As the airplane engine ordinarily has no flywheel, an object is to sodispose the material of the hub, that its weight and rigid'ty serve tosmooth out the irregular turning moment of the engine. This reducesvibration in the airplane and engine, and partially dampens its eifectbefore itreaches the blade as setting.

It is important to ach eve these objects, and make it possible to shiftthe pitch, or even reverse the propeller; with small expenditure ofeffort and attention on the part 40 of the operator. In airplanes,variable pitch propellers must be capable of shifting at highrevolutions in flight so as not to lose altitude.

It is not merely a case of strength of material; but the constructionmust possess in- ;3 herent strength. Loads like centrifugalsubstantially straight lines.

loads, must be carried along members having Such inherent strengthmust'be so great as to benot only sulficient; but strong to such adegree that the propeller hub, and all its parts, remain o rigid andinflexible under severe strain, regardless of the drastic limitations ofweight imposed by flight conditions. Maximum rigidity, and endurance,are qualities essential to the commercial success of the variable pitchairplane propeller. All mechanical motion in the shift mechanism shouldbe accurate, compact, and inherently balanced to at tain practicalsuccess. I particularly exclude as unworthy of engineering consideration3 any propeller without at least two distinct and separate bearingssupporting the root of each blade.

An object of the invention is to correct a common structural weakness inaircraft pro- 55 pellers of having a driving shaft pass through, orinto, the propeller blade casing.

To make the point clear about the difficult practical conditions ofservice, I will give the following practical example. In Army and Navytwo-bladed propellers, 89" in diameter, in actual use with approvedaircooled engines of 200 horse power 1800 revolutions per minute; thecentrifugal force, tending to tear a sixteen pound blade out by theroots is 30,000 lbs. Such propellers have blades adjustable on theground, firmly bolted in place, and made of Westinghousemicarta, amateriallighter than duralumin. If the blades were made of duralumin (27lbs. per blade), the blade root would require bearings that would permitshifting the pitch, when the centrifugal force is over 50,000 lbs. Now,25 tons may be ten times more than the weight of the whole airplane.forces acting on the blades would add approximately 50 percent, to thestresses imposed by the centrifugal force in each case.'

The example is .cited from a class of so called adjustable pitchpropellers. The 90 Other term, unfortunately, is partly a misnomer,since said pitch is only adjustable when the propeller is at rest. Inoperation, they perform precisely like solid non-adjustable propellers.They are more properly sectional propellers comprising hub and blades.

On the other hand, the variable pitch or controllable pitch class areadapted to changing the pitch in flight to meet the evolutions andoperating conditions of aerial navigation. The National AdvisoryCommittee for Aeronautics defines the terms variable pitch orcontrollable pitch as turning the blades to any desired pitch, while thepropeller is in rotation. Therefore, these terms must be so interpretedherein. Of course, the pitch of the blade may be changed incidentally,with the hub at rest,-zero revolutions.

A further object is to provide easy means for shifting the pitch of theblades; and yet, make the blades come near to without actually beingself-locking within the blade casing in any position into which they maybe moved. It is also important to indicate to the pilot the relativeposition of the-propeller blades, and the approved function of eachposition as take off, climb, economy etc. to suit particularinstallations. Pilots are not generally familiar with these technicalpoints.

The construction must be so simple that the number of parts approaches aminimum. The parts must also be compact so as to possess inherentstrength. All cranks, levers, and arms must be eliminated from therevolving propeller. The bearings usually associated with levers,cranks, arms, etc. are comparatively small, consequently are muchaffected by wear and tear. Such levers, cranks, etc. promote and augmentvibration. Two tenths of one degree variation in the pitch setting ofthe blades of a two-bladed propeller will often cause a seriousvibration communicated to the airplane structure.

An important object of the invention is to so construct, arrange, andassemble the hub that no openings are needed therein for the passage ofthe power shaft, assembly of shift gears, blade adjusting arms, or othershift mechanism. The small reinforced openings at the axial centertransmit no power from the power shaft. Attaining this object insures ahub of great inherent strength and stiffness per unit of weight.

Still another purpose is to totally enclose the pitch adjustingmechanism in a case that is forgeable, grease tight and water tight.This protects all that is good within the propeller, while keeping outall-dust,-dirt, rain, snow, or sleet.

In variable pitch propellers, it is sometimes important to vary thepitch setting down to zero; and then run into negative pitch angles, forthe purpose of reversing the thrust of the propellr This would occur,for example,

my. W

in landing aircraft on the ground, or alighting on the water. Provisionhas been made in my design to limit the maximum pitch angle in the aheadposition. Likewise, the pitch adjustment is stopped at some other pitchangle, when a minimum position is reached Of course, it must beunderstood that the engine usually turns in one direction only; and thatreversing the pitch angle of the propeller blades while the engine isrunning, efl'ects reversal in propeller thrust.

It has been customary in designing aircraft propellers of the variablepitch type, to insert the end of the engine shaft right into the hub ofthe variable pitch propeller. This means transmitting the engine powerthrough the centre of the propeller hub. I use a different method. Mymethod is to transmit the engine power through flange bolts to theoutside shell of the propeller casing, so as to obtain greater strengthand stiffness; while leaving the core, or heart, of the propeller hubfor the safe location of the smaller precision parts required for pitchustment. I eliminate engine twisting moment at the center of the hubcasing, which is a weak spot when pierced by the engine shaft. In thesense that the power shaft does not pass through the propeller casing;my propeller may be regarded as hubless, affording a virtually strongerconstruction with a given weight, than can be obtained by passing thepower shaft through the blade casing. Incidentally this sets thepropeller blades farther from the engine, aposition that adds a littleto the overall efliciency of the propeller installation.

How important this is can be gathered from the following example. Inpresent practice, a seven cylinder standard engine at full powertransmits over 100 impulses (explosions) per second directly to thepropeller, without the use of the usual flywheel to smooth out suchexplosive impulses. Pilots have referred to the effect as giving her thegun, on account of its similarity to the sound at full throttle to theroar of a machine gun. At any rate, these impulses have to be taken careof without variation in the pitch setting and pitch controllingmechanism. Success or failure depends upon how well the variable pitchmechanism is able to need ass be left largely to engineering judgment,de-

pendent upon the conditions of service.

It is common practice at the present time for aircraft engines to weightwo pounds per brake horse power. A propeller is expected to absorb thispower, and convert perhaps three-fourths of it into useful work, with aweight allowance of less than one-half pound per brake horse power.

The problem appears to be almost impossible of solution. Apparently noone has succeeded in producing an actual propeller capable of variablepitch, that can be said to be practical commercially. They are sometimesbuilt, used a few times, and then laid aside.

In general, it is my object to overcome the aforesaid difficulties witha practical com:

mercial construction.

My invention further comprises the details of construction, andarrangement hereinafter described, and claimed. Referring to theaccompanying sheets of explanatory .drawings, the same reference lettersin different views indicate identical parts.

Fig. l-shows a two-bladed propeller sectioned on a line with the axis ofa hollow power shaft, and in line withthe axis of the blades. The powershaft is shown broken off at the right.

Fig. 2 shows a half-section on the line mm, Fig. 1; with a half planview, having certain parts shown in section, other parts in full view,so as to illustrate the construction.

Fig. 3 is a section of the blade root on the line XX Fig. 1, showing howit is keyed to the gear, and to the inner race of the ball bearmgs.

Fig. 4 is a section through'the gear and splined shaft on the line 22,Fig. 1.

Fig. 5 is a side view of Fig. 1 from the left, with the hub cap removed,and the hollow hub broken away, showing the working parts of thevariable pitch mechanism.

Fig. 6 is a sectional detail show ng the character of stub gear teeth,shown in Figs. 1, 2, and 5.

Fig. 7 shows an outside elevation of the variable pitch propeller, theactuating lever, control rod, etc., in general relatiqn to an air? craftengine.

Fig. 8 is an enlarged detail of pitch control handwheel at a section ofinstrument board in the pilots cockpit. Apitch indithe blades to thepilot.

In Figs. 1 and 2, the end of the power shaft A, spreads out into aflange connection. The internal rod B, which serves as a shifting rodfor shifting the pitch of the propeller blades, has two cylindricalportions marked 1, provided with right hand, and left hand, spiralsplines. These right and left splines may be called herring bone splinesfor technically describing the construction.

The power shaft A, has a flange 2. The propeller hub has a hollow form,made in two similar halves, 3 and 4. The hub halves are preferably madeof heat treated steel with carburized ball races to secure specialhardness integral with the hub. A streamline cap 5, has a basecorresponding to flange 2, improving the contour, and providing asplined guide 5, for the shifting rod.

This cap has a series of six 6) fitted bolts marked 6, firmly boltingfour connected parts together. In addition to the six bolts, the splithub is firmly held together by standard ring clamps 7, having lugs 8,and bolts 9.

broken-off cylindrical roots, or shanks, of

the propeller blades, 10 and 11, are shown.

This particular propeller has two blades, but three or more blades arealso within the scope of the invention. The blades are made preferablyof either a solid or a hollow construction, of the lightest materialaffording the maximum strength per unit of weight, so as to avoidshifting extra weight.

The blades may have any suitable external propeller, or airfoil, formwith blade axis either straight radial, or curved slightly backward. Itis desirable to have the blades fairly wellbalanced about their ownaxes, as regards air pressure in operation.

The round root of blade 10 in Fig. 1, is firmly attached to the gear 12,by a special threading 13, of a prolongation of the gear body. These arekeyed together with a sleeve continuation of the ball bearing races bykey 14, shown'in side view, in Fig. 3. The keyway is cut at any properblade position, and the key fitted into place. Finally, the key itselfis made fast by the locking wires 15, as shown in Fig. 3.

A threaded axial hole 16, is provided for any convenient purpose likeinserting a shown shrunkonto the blade root; but it may preferably bescrewedon, to do its share of holding the blade. The sleeve 19, isgrooved and threaded like a fluted nut for helping to hold the bladefirmly within the propeller hub, so as to resist the great centrifugalforce tending to throw the blades apart. The blade is held firmly bysleeves numbered 18-and 19,

gear 12, and key 14.

Theball bearings are of a type adapted to take care of both the endthrust, tending to tear the blade out by the roots, and the side loadscommunicated by the shaft, and thrust bending loads on each blade.

The ball bearings serve to evenly distribute all these forcescircumferentially, and eliminate friction. They serve a double purposeof holding the blades in the hub against centrifugal force, While theymake it possible to shift the pitch of the blades with a minimum ofefiort.

The bevel gears shown inside the propeller in Figs. 1 and 5, arepreferably made of a chrome-nickel steel, heat-treated to obtaintoughness and wear. They reinforce the blade roots, and reinforce theholding power of the blade sleeves. However, gears marked 21, operatingon the right and left hand splined rods, may be made of a toughmanganese bronze, as being more readily manufactured of that material.High tensile bronze is an excellent material for absorbing shock comingfrom the teeth of the steel gears at the roots of the blades.

The cutting of the bevel gearteeth is important. -These gears must becut to an accurate fit. They must mesh closely together, see Fig. 6.There must be no back-lash or lost motion. Ordinary cut gears are givena certain amount of clearance. The teeth in my gears must meshaccurately into each other without any play. After being shifted, thegears serve to hold the blades in the established position regardless ofthe complex forces acting upon the blades. They do not serve to transmitpower to the blades. They hold the blades in the correct positionaccording to the pilots'setting.

The gears illustrated hereimFigs. 2 and 5,

are what are known as straight bevel gears.

They are the simplest to make. It is also possible to use what are knownas spiral bevel gears. The teeth should preferably be of the stub toothform approximately shown in Fig. 6. This form allows the gears to bemeshed close together without the risk of jamming their action. Thecombination of hard steel gears in the blade roots, with a softermaterial such as bronze in the spline shaft gears, is desirable forpractical accurate meshing.

In Fig. 1, the internal shifting rod B, with its spiral splined portionsmarked 1, always turns with the propeller hub and hollow power shaft A.The inside surface of the hollow end 1, is channeled to slide accuratelyupon a grooved projection on the inside of the propeller cap 5, see Fig.4, showing a cross section on the line 22 in Fig. 1. The groovedprojection compels the shifting rod B, to slide forward or back, in anaccurate line parallel to the axis of hollow shaft A, when the pilotshifts the blades of the propeller. The grooved projection, and the pinin the shaft slot, guide the shifting rod B, at both ends against rotarymovement relative to engine shaft and propeller. Holes 20, are drilledinto the grooved projection inside the cap, to equalize any pressuredifference in the connecting spaces while moving the shifting rod. Nogreat importance is attached to the use of such holes.

One of the bevel gears 21, in Fig. 1, may also be seen in axial view inFig. 5. The latter view shows clearly that a portion of each side ofthese gears has been cut away to save weight.

In Fig. 1, the hollow end portions 1, of the shifting rod have twoexternal spiral cams (splines) out upon them, one being a right, and theother a left hand spiral. Each cam consists of a series of eight or morespiral splines, that are more nearly axial in direction thancircumferential. This herringbone arrangement of the spiral splines isselfbalancing for holding the blades in position. For small spiralangles of the herring-bone splines, the mechanism is self-locking withinthe blade casing, independent of the hand wheel screw. This arrangementmakes the cams easy to shift in an axial direction, when shifting therod. The multiple series provide abundant wearing surface, and themaximum of strength; since ordinarykeyways would soon wear out, andtwist out, with severe stresses encountered in practice. This series ofspiral cams engage corresponding spiral cams projecting inside thehubsof the two bevel gears 21, slidably mounted thereon. see Figs. 1 and4. Shifting the guided rod B, compels the two bevel gears 21, to followthe spiral cams; thus turning said gears in balance accurately inopposite directions, and varying the pitch of the propeller blades. Itis desirable to provide the smooth right end of the shifting rod 1, inFig. 1, with a bronze sleeve to get one of the gears, 21, on thesplines; or else spline the whole right end.

9 tion.

It should be noted in Figs. 1 and 2, that the hub halves, 3 and 4;, aremade in one piece, that their cross sections are unimpaired in strengththroughout their length; and that the radial portions of such hubs areinterconnecessary. In general, it is advisable not to provlde more pitchrange in either the ahead or reverse position than the service inindividual aircraft requires. Small pitch ranges are preferred, becausethen it is easier nected by substantially straight lines of the to shiftthe pitch by using less spiral angle in central portion. Such is thebest means to withstand the enormous centrifugal force tending to throwthe blades apart in opera- As drawn in Figs. 1, 2 and 7, the propellerblades are shown in What is known as the neutral or mid-position, wheretheir twisted surfaces cause no resultant axial thrust with power shaftturning. Such mid-position may be represented diagrammatically by theline OM in Fig. 2. With the power shaft turning as indicated by thearrow at the right of Figs. 1 and 2, and moving the shifting rod B tothe right, I would throw the top blade of the propeller into theposition LL, and the opposite blade into the position LL. Thesepositions of the blade would represent the ahead position of a left handpropeller, causing an axial pull on the shaft toward the left in Figs.1, 2, and 7.

Again, when the shifting rod B is moved to the left in Figs. 1 and 2,the top blade of the propeller would move into position LL, and theopposite blade into the position LL Such would be the reverse positionof a left hand propeller causing an axial thrust on the shaft toward theright in Figs. 1, 2 and 7.

It thus becomes apparent that by setting the position of the shiftingrod B, I can cause the blades to assume any given pitch from full pitchahead, through the neutral or midposition, to full pitch reverse.

In order to make explanation as simple as possible, the illustrationsindicate a range of movement of approximately the same amount of pitchangle in the forward, as in the re-.. verse position. In otherjwords, inFig. 2 the arc F equals the are R. In zactual practice, itis better tochoose a neutral position so as to give perhaps twice as much pitchrange in the ahead position as in the reverse. In the ahead position,the pilot requires plenty of range for pitch adjustment. When flying ata high altitude in light air, with aircraft provided with a superchargerfor compressing the air taken in by the carburettor, the pilot mayincrease the propeller pitch and the aircrafts speed without running theengine revolutions above the normal at sea level. By choosing smallspiral angles for herrin bone splines, the blade settings may be ma eall positive, for example plus 10 to 20 degrees. By choosing a spiralangle of about 10 de recs, it is possible to give a range of pitch adustment to the blades from some negative setting, like minus tendegrees, to a plus setting of say twenty-five degrees. It

is even possible to go beyond these points if herring bone splines.

Figs. 1 and-2, at the right, show a simple way of. moving the shiftingrod B, for which no particular claims in this specification are made.

For other improvements of this propeller, see applicants co-pendingapplication, Se-

rial 476,0,96, Aug. 18th, 1930.

An adapter ring 22, is bolted to the engine housing. A lever box 23, inhalves, is attached thereto. A forked lever 24, with fulcrum pin 25,operates a thrust ring 26, working on a sliding collar 27, having across-head pin 28, passing through slots 29, in hollowshaft A. Thiscross-head pin alsov passes tightly through the internal shifting rod B,.but moves freely in slots 29, in the hollow shaft A. Thus when lever 24is moved, it causes a. corresponding axial movement of the internalshifting rod B, regardless of the turning of the power shaft. It isapparent that the internal shifting rod B, has a balanced motion insliding; and yet is guided by the pin and slot, 29, at one end, and bythe grooved projection, 5, at the other end. This is for stiffness,accuracy, and safety. A rod 30, pin connected to the end of forked lever24, holds the lever in a fixed position, or communicates controlmovements from the pilots cockpit. Of course, it is preferable to buildthe lever box 23, especially its lower half, in one piece with theengine crankcase, thus securing the greatest strength with a minimum ofwelght.

Fig. 7 illustrates the variable pitch propeller in a neutral position,mounted diagrammatically in front of an air-cooled engine E, indicatedin dotted lines, with pitch control rod 30 broken, but its continuationto a larger scale is shown in Fig? 8. The rod 30 is expected to passconveniently between any adj acent engine cylinders in actual practiceFig. 8 shows a sectional elevation of an instrument board 31, in thepilot's cockpit. A balanced handwheel 32, with handle 33, is keyed to aleft hand screw 34,.ori the back of the instrument board. The pitchcontrol rod 30 has a crosshead, 35, Welded to it. This crosshead isthreaded to suit the left hand screw 34, and slides over the squareguide 36. When the pilot moves the handwheel clockwise, it moves thecrosshead, 35, away from him. Such movement actuates the control rod30,.so as to increase the pitch of the left .hand variable pitchpropeller. Again, when the pilot moves the handwheel counter clockwise,he decreases the pitch, and may even reverse the pitch of the propeller,The hand wheel 32, may be turned by hand or power.

The two collars 37 in Fig. 8, are pinned to the handwheel screw 34. Thecollars are provided with awe, which circumferentially meetcorresponding jaws on the travelling crosshead 35, and stop its motionat either end without causing the screw mechanism to am.,

B this arrangement, definite stops are set in t e hand control, limitingthe setting of the pitch of the propeller blades in the ahead andreverse positions.

In Fig. 8 is shown a fitting 38, welded to the control rod 30, and havina pin connection with an eye on the end 0 a flexible tube 39. Thisflexible tube 39, passes through, and in front of, an indicator scale40, in the 'pilots cockpit. The flexible tube mounts a double index 41,reading on the indicator scale. The lower indicator scale may read bladepitch angles in degrees, or in feet of propeller pitch; while the upperscale might conveniently indicate corresponding economy, cruising, fullspeed, maximum pitch, neutral and reverse. The indicator may beilluminated. It can be arranged so that a pilot could also feel theposition of the index with his fingers, in the dark.

It must be evident from Fig. 8 and the construction of the variablepitch propeller, that the blade setting remains fixed when the pilot isnot touching the handwheel 32. The handwheel needs attention only whenshifting the propeller blades at will. The simple indicator, serving onepurpose, and extremely light in weight, is of inestimable value to thepilot for instantaneous informa tion, in operating both pitch and enginecontrols in flight.

There are certain advantages in a pitch control operating with ahandwheel and screw. It gives a certain amount of slowness and accuracyto the control, articularly desirable 1n training planes, and orstudying propeller performance in actual flight.

In accordance with the provisions of the patent statutes, I havedescribed herein the general principle of construction, and operation,underlfying my invention; together with one form 0 apparatusrepresentative of its embodiment. I desire to have it understood thatsuch form is only illustrative, and that the invention may be carriedout by other means within the urview of the invention.

Also, while it is desired to use the various feahaving their rootsentered in said hub, ballbearing means engaged between said hub andblade roots to sustain the centrifugal load on said blades and to reducefriction of axial rotation thereof, a shifting rod axially movablewithin said power shaft, separate counter balancing right and leftspiral splines carried by said shifting rod, cooperating gears connectedbetween respective bladeroots and the right and left hand spiral splinesrespectively, and means for manually actuating said shifting rod.

2. In a controllable pitch propeller, the combination of an inclosinghub in two halves with axially rotatable propeller blades having rootsinclosed by said hub, means including through bolts to secure said hubin swivelin relation to said blade roots, a plurality o spacedball-bearing sets engaged between said hub and blade roots to sustainthe centrifugal and bending loads on said blades and to reduce frictionof axial rotative movements thereof, and means to impart swivelingmovements to said blades with propeller in operation.

3. In a controllable pitch propeller, a radial hollow hub splitlongitudinally with the blade axes and adapted to be driven by a powershaft, axially rotatable propeller blades having roots entered in saidhub, ballbearing means engaged between races of said hub and bladesleeve races, reinforce rings driven bevel gear fixed to the inner endof each blade root, a pair of driving bevel gears within said hub tomesh respectively with opposite sides of said driven bevel gears, rightand left hand multiple spiral splines engaged respectively with saidrespective driving bevel gears and axially slidable in relation theretoa hollow power shaft connected with said hub, a shifting rod movable insaid shaft for sliding said splines, and means for manually actuatingsaid shifting rod.

5. In a variable pitch propeller, a hollow power shaft, a hollow hubadapted to be driven by said shaft, axially rotatable proeller bladeshaving roots entered in said ub, counterbalanced transmission meanscentrally disposed within said hub for rotating said blades, saidtransmission means including a pair of multiplespiral right and lefthand splines, a shiftin rod to carr and move said splines, said s iftingrod eing axially slidable in said power shaft and hub, and meansadjacent to said hub for moving said shifting rod.

6. In a variable pitch propeller, a hollow power shaft, a hollow hubadapted to be driven by said shaft, axially rotatable propeller bladeshaving roots entered in said hub, counterbalanced transmission meanscentrally disposed within said hub for rotating said blades, saidtransmission means including a pair of multiple spiral right and lefthand splines, a shifting rod to carry and move said splines, saidshifting rod being axially slidable in said power shaft and hub, across-head pin connected with said shifting rod, said hollow shafthaving slots through which said cross-head pin extends, and meansexteriorly adjacent to said hub engaged with said cross-head pin formanually actuating said shifting rod- 7. In a variable pitch propeller,the combination with a power shaft of a hollow hub, means for fixedlycoupling said hub to the free end of said shaft. said hub having radialbearing portions, axially rotatablepropeller blades having rootsjournaled in said bearing portions, a shifting rod axially movable insaid hub, said rod having herring-bone spiral splines, and bevel gearingactuated by said splines and connected with said blade roots foreffecting pitch adjustments of said propeller blades.

8. In a controllable pitch propeller, an inclosing hollow hub in twohalves having split radial bearing portions in the line of divisionthereof, an abutting power shaft, a

flange face for fixedly coupling said hub to a flanged end of saidshaft, through-bolts for securing said hub in assembled condition and tosaid shaft end, externally reinforcing rings to secure said bearingportions against separation, axially rotatable propeller blades havingroots entered in said bearing portions, said bearing portions havinginternal annular ball races integrally formed therewith, opposing ballraces aifixed to said blade roots, and ball sets between opposed races.

9. In a variable pitch propeller provided with axially rotatable bladesjournaled in radial bearing portions of a hollow hub, a slidableshifting rod entered in said hub, an axially splined guide means forsaidrod, right and left hand spiral splines fixed on said rod, and bevelgearing actuated by said spiral splines to transmit axially rotativeadjusting movement to said propeller'blades.

10. In a variable pitch propeller, a hollow power shaft flange connectedto a hollow hub having radial bearing portions, axiallv rotatablepropeller blades journaled in said bearing portions, a plurality of setsof ball bearings engaged between said bearing portions and the journaledportionsof each of said blades, said ball-bearing sets being adapted tosustain centrifugal thrust and rotational power stresses of said blades,and concentric blade pitch adjusting means axially disposed within saidhub so as to rotate therewith.

11. A variable pitch propeller having in combination, a hollow hubhaving radial bearing portions, ball-bearings in said bearing portions,propeller blades having roots j ournaled by said ball-bearings andsustained thereby against centrifugal stresses, a nose cap aflixed tothe one side of said hub, a power shaft aflixed to the other side ofsaid hub, a shifting rod having three sets of splines comprising axialguide splines working in said nose cap, right hand spiral splines andleft hand spiral splines, a pair of driving bevel gears respectivelyengaged by said right and tion balls between opposed races, means for.

securing said hub and its bearing portions in assembled relation, bevelgears having axial projections threaded into the inner end portions ofsaid blade roots, and a concentric transmission means axially disposedwithin said hub and cooperating with said bevel gears to impart pitchadjusting movement to said blades.

13. In a variable pitch propeller provided with axially rotatable bladesjournaled in radial bearing portions of a hollow hub, a slidableshifting rod entered centrally into said hub, an axially splined guidemeans for said rod, right and left hand spiral splinesdisposedexternally on said rod, bevel gearing actuated by said spiralsplines to transmit pitch adjusting movement to said blades, a hollowpower shaft around the exteriorly extending portion of said shiftingrod, means for securing said hub to the free end of said power shaft,said rod having a cross-head, said power shaft having longitudinal slotsin its walls through which the ends of said cross-head project, a swivelring means connected with said cross-head ends, actuating levermechanism connected with said swivel ring means, and manually operablemeans for moving said lever mechanism.

14. In a controllable pitch aircraft propeller, a split hub member ofrectangular box section in its central portion and of circular crosssection in its radial portions, including split ball races swivelablymounting multiple blades in ball bearings, and having reinforced ringsat each radial portion; said central portion forming two flange elementswith registering bolts mating with a, flange element of a power shaft:whereby said shaft is excluded from the hub, the blade-roots areconfined to a turning movement, a pitch setting mechanism is completelyhoused, and the power stress removed from the center of the hub.

In testimony whereof I afiix my signature.

EMIL A. BRINER.

